Coverage Analyzer Skill

Purpose

This skill provides comprehensive test coverage analysis, gap identification, threshold validation, and detailed reporting to ensure code quality and adequate test coverage across the codebase.

When to Use

• Measuring test coverage for a module or project

• Identifying untested code and coverage gaps

• Validating coverage meets threshold (≥ 80%)

• Generating coverage reports for review

• Analyzing coverage trends over time

• Finding missing branch coverage

Coverage Analysis Workflow

1. Basic Coverage Measurement

Run Tests with Coverage:

Install pytest-cov if not installed

pip install pytest-cov

Basic coverage measurement

pytest --cov=src tests/

Coverage with terminal report

pytest --cov=src --cov-report=term tests/

Coverage with missing lines

pytest --cov=src --cov-report=term-missing tests/

Coverage for specific module

pytest --cov=src.tools.feature tests/

Quick Coverage Check:

Show percentage only

pytest --cov=src --cov-report=term tests/ | grep TOTAL

Check if coverage meets threshold

pytest --cov=src --cov-fail-under=80 tests/

Quiet mode with coverage

pytest --cov=src --cov-report=term -q tests/

Deliverable: Basic coverage metrics

2. Detailed Coverage Analysis

Generate Detailed Reports:

HTML coverage report (most detailed)

pytest --cov=src --cov-report=html tests/

Open htmlcov/index.html in browser

XML coverage report (for CI/CD)

pytest --cov=src --cov-report=xml tests/

JSON coverage report

pytest --cov=src --cov-report=json tests/

Multiple report formats

pytest --cov=src
--cov-report=html
--cov-report=xml
--cov-report=term-missing
tests/

Analyze Coverage by Module:

Show coverage for each file

pytest --cov=src --cov-report=term tests/

Coverage with line numbers

pytest --cov=src --cov-report=term-missing tests/

Annotated source files

pytest --cov=src --cov-report=annotate tests/

Creates .py,cover files with coverage annotations

Deliverable: Detailed coverage reports

3. Coverage Gap Identification

Find Untested Code:

Show missing lines

pytest --cov=src --cov-report=term-missing tests/

Show missing branches

pytest --cov=src --cov-branch --cov-report=term-missing tests/

Generate HTML report to visualize gaps

pytest --cov=src --cov-report=html tests/

Open htmlcov/index.html to see line-by-line coverage

Identify Low Coverage Modules:

Run coverage and parse output

pytest --cov=src --cov-report=term tests/ | grep -v "100%"

Find files below 80% coverage

pytest --cov=src --cov-report=term tests/ | awk '$NF ~ /%/ && $NF+0 < 80'

Sort by coverage percentage

pytest --cov=src --cov-report=term tests/ | sort -k4 -n

Analyze Coverage by Test Type:

Coverage from unit tests only

pytest --cov=src --cov-report=term tests/unit/

Coverage from integration tests only

pytest --cov=src --cov-report=term tests/integration/

Combined coverage

pytest --cov=src --cov-report=term tests/unit/ tests/integration/

Incremental coverage (append mode)

pytest --cov=src --cov-append --cov-report=term tests/unit/ pytest --cov=src --cov-append --cov-report=term tests/integration/

Deliverable: Coverage gap analysis

4. Branch Coverage Analysis

Measure Branch Coverage:

Enable branch coverage

pytest --cov=src --cov-branch --cov-report=term-missing tests/

Branch coverage with HTML report

pytest --cov=src --cov-branch --cov-report=html tests/

Show partial branches

pytest --cov=src --cov-branch --cov-report=term-missing tests/ | grep "!->"

Analyze Conditional Coverage:

Find untested conditionals

pytest --cov=src --cov-branch --cov-report=term-missing tests/ | grep "if"

Check switch/case coverage

pytest --cov=src --cov-branch --cov-report=term-missing tests/ | grep "case"

Deliverable: Branch coverage metrics

5. Coverage Threshold Validation

Validate Minimum Coverage:

Fail if coverage below 80%

pytest --cov=src --cov-fail-under=80 tests/

Fail if coverage below 90%

pytest --cov=src --cov-fail-under=90 tests/

Check with specific threshold and report

pytest --cov=src --cov-fail-under=80 --cov-report=term-missing tests/

Per-Module Thresholds:

Core logic: 90% minimum

pytest --cov=src.core --cov-fail-under=90 tests/

Utilities: 85% minimum

pytest --cov=src.utils --cov-fail-under=85 tests/

Interfaces: 80% minimum

pytest --cov=src.interfaces --cov-fail-under=80 tests/

Deliverable: Threshold validation report

6. Coverage Configuration

Configure .coveragerc:

.coveragerc

[run] source = src omit = tests/* */init.py /venv/ /.venv/ /migrations/

branch = True

[report] exclude_lines = # Default pragmas pragma: no cover

# Don't complain about missing debug-only code
def __repr__
def __str__

# Don't complain if tests don't hit defensive assertion code
raise AssertionError
raise NotImplementedError

# Don't complain if non-runnable code isn't run
if __name__ == .__main__.:
if TYPE_CHECKING:

# Don't complain about abstract methods
@abstractmethod

precision = 2 show_missing = True

[html] directory = htmlcov

[xml] output = coverage.xml

Configure pyproject.toml:

pyproject.toml

[tool.coverage.run] source = ["src"] omit = [ "tests/", "/init.py", "/venv/", "/.venv/", ] branch = true

[tool.coverage.report] exclude_lines = [ "pragma: no cover", "def repr", "raise AssertionError", "raise NotImplementedError", "if name == .main.:", "if TYPE_CHECKING:", "@abstractmethod", ] precision = 2 show_missing = true fail_under = 80

[tool.coverage.html] directory = "htmlcov"

[tool.coverage.xml] output = "coverage.xml"

Deliverable: Coverage configuration

7. Coverage Reporting

Generate Coverage Reports:

Terminal report

pytest --cov=src --cov-report=term tests/

Terminal report with missing lines

pytest --cov=src --cov-report=term-missing tests/

HTML report for detailed analysis

pytest --cov=src --cov-report=html tests/

XML report for CI/CD integration

pytest --cov=src --cov-report=xml tests/

JSON report for programmatic access

pytest --cov=src --cov-report=json tests/

All reports

pytest --cov=src
--cov-report=term-missing
--cov-report=html
--cov-report=xml
--cov-report=json
tests/

Coverage Summary Report:

Coverage Report

Overall Coverage: 87%

By Module

Critical Gaps

1. Error handling in src.core.process() (lines 45-47)
2. Edge case validation in src.utils.validate() (lines 67-70)
3. Exception paths in src.interfaces.execute() (lines 56-58)

Recommendations

• Add tests for error conditions in core module
• Improve edge case coverage in utilities
• Test exception handling in interfaces

Status

✅ Overall coverage: 87% (target: 80%) ✅ Core business logic: 95% (target: 90%) ✅ Utilities: 88% (target: 85%) ✅ All thresholds met

Deliverable: Comprehensive coverage reports

8. Coverage Trend Analysis

Track Coverage Over Time:

Generate coverage badge

pip install coverage-badge coverage-badge -o coverage.svg

Save coverage history

pytest --cov=src --cov-report=json tests/ mv coverage.json coverage-$(date +%Y%m%d).json

Compare coverage between runs

coverage json python -c "import json; print(json.load(open('coverage.json'))['totals']['percent_covered'])"

Coverage Diff:

Coverage for current branch

pytest --cov=src --cov-report=json tests/ cp coverage.json coverage-current.json

Coverage for main branch

git checkout main pytest --cov=src --cov-report=json tests/ cp coverage.json coverage-main.json

Compare

diff <(jq '.totals.percent_covered' coverage-main.json)
<(jq '.totals.percent_covered' coverage-current.json)

Deliverable: Coverage trends and comparisons

Coverage Analysis Patterns

Quick Coverage Check

Fast coverage check during development

pytest --cov=src --cov-report=term-missing -q tests/unit/

Comprehensive Coverage Analysis

Full coverage analysis with all reports

pytest --cov=src
--cov-branch
--cov-report=html
--cov-report=xml
--cov-report=term-missing
--cov-fail-under=80
tests/

CI/CD Coverage Check

Coverage check for CI/CD pipeline

pytest --cov=src
--cov-report=xml
--cov-report=term
--cov-fail-under=80
tests/

Coverage Gap Investigation

Find and analyze coverage gaps

pytest --cov=src --cov-report=html tests/

Open htmlcov/index.html

Click on files with low coverage

Review highlighted untested lines

Coverage Metrics and Thresholds

Coverage Targets

By Module Type:

• Core Business Logic: ≥ 90%

• Services/APIs: ≥ 85%

• Utilities/Helpers: ≥ 85%

• Models/DTOs: ≥ 90%

• Interfaces/Contracts: ≥ 80%

• CLI/Main: ≥ 70%

By Coverage Type:

• Line Coverage: ≥ 80%

• Branch Coverage: ≥ 75%

• Function Coverage: ≥ 85%

Overall Project:

• Minimum: 80%

• Target: 85%

• Excellent: 90%+

Acceptable Exclusions

Acceptable to exclude from coverage

def repr(self): # pragma: no cover return f"Object({self.id})"

if name == "main": # pragma: no cover main()

if TYPE_CHECKING: # pragma: no cover from typing import Optional

@abstractmethod def interface_method(self): # pragma: no cover pass

def debug_helper(): # pragma: no cover # Debug code not run in production pass

Coverage Analysis Checklist

Pre-Analysis

• Tests are running and passing

• pytest-cov installed

• Coverage configuration set (.coveragerc or pyproject.toml)

• Exclusions configured properly

Analysis

• Line coverage calculated

• Branch coverage calculated

• Coverage by module analyzed

• Coverage gaps identified

• Critical gaps prioritized

Threshold Validation

• Overall coverage ≥ 80%

• Core business logic ≥ 90%

• Utilities ≥ 85%

• No critical code untested

• Branch coverage ≥ 75%

Reporting

• Terminal report generated

• HTML report generated (for detailed review)

• XML report generated (for CI/CD)

• Coverage summary documented

• Gaps documented with recommendations

Common Coverage Commands

Quick Reference

Basic coverage

pytest --cov=src tests/

Coverage with gaps

pytest --cov=src --cov-report=term-missing tests/

Coverage with threshold

pytest --cov=src --cov-fail-under=80 tests/

Branch coverage

pytest --cov=src --cov-branch --cov-report=term-missing tests/

HTML report

pytest --cov=src --cov-report=html tests/

Full analysis

pytest --cov=src
--cov-branch
--cov-report=html
--cov-report=term-missing
--cov-fail-under=80
tests/

Coverage Analysis Troubleshooting

Coverage Tool Not Found

Install pytest-cov

pip install pytest-cov

Verify installation

pytest --version pip show pytest-cov

Incorrect Coverage (Too Low/High)

Check source configuration

cat .coveragerc cat pyproject.toml

Verify source parameter

pytest --cov=src tests/ # Correct pytest --cov tests/ # Wrong - testing test code

Clear coverage cache

rm -rf .coverage htmlcov/ pytest --cov=src tests/

Missing Files in Coverage

Check omit configuration

grep -A5 "[run]" .coveragerc

Verify files are imported

pytest --cov=src --cov-report=term tests/ | grep "filename"

Check test imports

grep -r "^import|^from" tests/

Branch Coverage Not Working

Enable branch coverage

pytest --cov=src --cov-branch tests/

Check configuration

grep "branch" .coveragerc

Verify branches exist

grep -r "if|else|elif" src/

Integration with Test Runner Specialist

Input: Completed test execution with coverage enabled Process: Analyze coverage, identify gaps, validate thresholds Output: Coverage report with gap analysis and recommendations Next Step: Report to test-runner-specialist for decision

Coverage Analysis Best Practices

Development

• Check coverage frequently during TDD

• Aim for >90% coverage on new code

• Review coverage reports locally

• Fix coverage gaps before committing

Pre-Commit

• Verify coverage meets threshold

• Review coverage diff vs main branch

• Ensure new code is well tested

• Check branch coverage for complex logic

CI/CD

• Generate coverage reports for every build

• Fail build if coverage below threshold

• Track coverage trends over time

• Archive coverage reports

Review

• Focus on critical paths first

• Prioritize business logic coverage

• Don't chase 100% coverage unnecessarily

• Exclude unreachable code appropriately

Coverage Gap Prioritization

High Priority (Fix Immediately)

• Core business logic uncovered

• Error handling paths untested

• Security-critical code uncovered

• Data validation missing tests

• API endpoints without tests

Medium Priority (Fix Soon)

• Utilities with <80% coverage

• Branch coverage gaps in logic

• Edge cases not tested

• Configuration parsing untested

Low Priority (Fix When Possible)

• Representation methods (repr, str)

• Debug/logging code

• CLI help text

• Non-critical utilities

Acceptable to Exclude

• Abstract methods

• TYPE_CHECKING blocks

• if name == "main"

• Platform-specific code not running in CI

• Deprecated code scheduled for removal

Supporting Resources

• pytest-cov documentation: https://pytest-cov.readthedocs.io

• coverage.py documentation: https://coverage.readthedocs.io

• Coverage best practices: https://testing.googleblog.com

• Sample .coveragerc: In project root

Success Metrics

• Coverage calculated accurately

• Overall coverage ≥ 80%

• Critical code coverage ≥ 90%

• Coverage gaps identified

• Reports generated successfully

• Thresholds validated

• Recommendations provided